A so called start-stop or idle-stop arrangement is based on the concept of halting combustion in a vehicle's engine during vehicle standstill (e.g. when waiting for a traffic light to change from red to green). Such an arrangement may allow for substantial savings in fuel consumption. For mixed highway/rural and city driving savings of at least 2-4% are feasible and for city driving savings of up to 10% are feasible.
Some previous attempts to provide such arrangements have been based on belt drives or have been starter based. Starter based systems are low cost and scalable to all sizes and kinds of power-trains but have two major drawbacks. On the one hand they cannot be engaged during engine ramp down and on the other hand they are quite noisy due to engagement noise and cranking noise.
One previous attempt at addressing the above problems with starter based systems is provided by JP 2000 274337, which describes a starting device for a vehicle, such as an idle stop car or a hybrid car, which starting device is especially suited for noise reduction. The starting device is provided with a pinion gear on the output shaft of an electric motor.
A ring gear is engaged and always meshes with the pinion gear. Between the ring gear and a crankshaft is arranged a one-way clutch which intervenes between the ring gear and the crankshaft, and which is arranged to permit only the transmission of driving force from the side of the electric motor to the internal combustion engine for starting thereof. The one-way clutch is built in between the ring gear and a flywheel of the internal combustion engine. In order to reduce the noise generated, the dental rate of engagement and engagement precision are raised, which is enabled through the ring gear being engaged and always meshing with the pinion gear.
Although JP 2002 74337 addresses the noise and engagement problems by the ring gear engaging and always meshing with the pinion gear a new problem is introduced. As the internal combustion engine of an idle stop vehicle or a hybrid vehicle will be brought to start automatically, e.g. by an onboard computer, the number of hourly starts and stops will be quite considerable, especially during city driving. This is likely to put considerable strain on the one-way clutch of the starter arrangement. Thus, it is not desirable to have the one-way clutch built in between the ring gear and the flywheel of the internal combustion engine according to JP 2002 74337, but would be preferable to arrange the one-way clutch directly at the crankshaft, in order to provide a smaller and more compact arrangement which could be applicable to a lager number of existing internal combustion engines.
However, it has been found that in order to appropriately affix a hub of the one-way clutch to the crankshaft the hub may be press fitted thereupon using special tooling applying considerable force. This makes it cumbersome to mount the one-way clutch, and certainly even more cumbersome to dismount and service the arrangement at an ordinary garage.